TLR4 and serum lipopolysaccharide activity: Additionally, researchers have found that IH in OSA is characterized by an altered gut-liver axis, which is characterized by increased intestinal permeability, endotoxemia, and overexpression of the endotoxin receptor TLR-4 by hepatocytes, Kupffer cells and hepatic stellate cells (HSCs), which are key features of NASH and fibrosis in NAFLD.